Bone cancer significantly decreases the quality of life of millions of cancer patients each year. A major problem in designing new therapies to treat this chronic pain was that until recently there was not a model available to define the mechanisms that generate and maintain bone cancer pain. The major thrust of this proposal is to use a rat tumor model that is mixed in nature (in that it induces both bone formation and destruction) to define the mechanisms that give rise to bone cancer pain that arises from mixed tumors such as breast or prostate when they metastasize to bone. Rat mammary carcinoma cells, stably transfected with green fluorescent protein, will be injected and confined to the intramedullary space of the rat femur. Over a twenty eight day period these tumor cells proliferate and induce bone formation, bone destruction, bone cancer related pain behaviors and a set of neurochemical changes in both sensory and spinal cord neurons that appears to be involved in generating and maintaining bone cancer pain. Using this model we will define: the time course and extent of tumor growth, bone formation, bone destruction, osteoclastogenesis, and bone cancer pain related behaviors (Aim 1): how the sensory and sympathetic innervation of bone changes as the tumor fills the intramedullary space, the bone is remodeled and bone cancer pain develops (Aim 2); the neurochemical changes that occur in primary afferent sensory neurons, sympathetic neurons, the spinal cord and dorsal column nuclei as the tumor grows, tumor induced bone remodeling occurs and bone cancer pain develops (Aim 3); whether systemic or intrathecal administration of morphine, COX-2 inhibitor, gabapentin or endothelin A receptor antagonist reduce specific aspects of bone cancer pain related behaviors, tumor growth, bone remodeling, osteoclastogenesis and the neurochemical changes that occur in the peripheral and central nervous system (Aim 4). Information from these investigations should expand our understanding of the mechanisms that generate and maintain bone cancer pain and lead to the development of more effective therapies for treating bone cancer pain.